This invention relates to image reading systems, and, more particularly, to an image reading system utilizing a machine or computer vision system.
Machine or computer vision systems generally utilize an array of light sensitive pixels which produce a signal output. When the array is scanned, an analog output pulse train is produced which may subsequently be processed. Subsequent processing generally includes converting the analog signals to digital signals which are then fed to a central processing unit (CPU) for analysis of the data, depending on the functions of the system, which can be numerous and varied. In manufacturing or inspection processes, the image data can be compared to stored calculated geometric or mathematical values as in U.S. Pat. No. 4,697,245 of Kara et al, and any differences represent errors or other aberrations. Thus, a part shape, size, location, or movement can be monitored continuously and any error detected can be used to generate a corrective signal for the making or moving of the items being inspected. For example, in a bakery, the system can be used to monitor the size of loaves of bread. Such an arrangement can even be used to monitor the number of raisins placed in a box of cereal. In metal stamping, the system can be used to inspect part edges, thus gauging the accuracy of the cutting edges of the die, and monitoring die wear.
In most manufacturing processes today, products are produced at a rate that exceeds the ability of humans to inspect precisely by eyeballing. Thus, in a bottling plant, determining the presence and orientation of labels on the bottles is extremely difficult using human visual inspection, because of the speed of movement of the bottles.
The ability to detect and track movement is one of the more useful features of machine or computer vision systems. In U.S. Pat. No. 4,748,502 of Friedman et al there is shown a system for detecting and reading eye movements, for use by physically handicapped people to enable them to communicate. Thus, on a first scan, the cornea and pupil of the eye may be in one position, and for a subsequent scan, in a second, different position. Where the user is reading an alphabet board, for example, having a known configuration, the system is able to correlate the eye position and movement with the letters being looked at, thereby enabling the user to spell out words.
One problem in machine vision systems, regardless of application, is the need for sufficient illumination to enable the array of light sensitive elements to activate. Generally, a form of steady state illumination is used, however, this represents an uneconomical solution to the problem. In U.S. Pat. No. 4,737,857 of Rucci et al, there is shown an arrangement for synchronizing the on/off light source with the optical scan of the device. The Rucci et al arrangement, however, is not typical of prior art vision systems.
Another problem with machine vision systems, especially where used to track moving objects, but also where the item being inspected or checked occupies a very small portion of the frame or raster as defined by the columns and rows of pixels, is the time spent in scanning or reading the entire array, when only a small portion thereof is involved. The Friedman et al patent recognizes the problem, but proposes no implementation of a solution for the problem.
There are numerous applications for machine vision systems, including, in addition to those already discussed, bar code readers and vehicle guidance systems, however, in prior art arrangements the size, complexity, and cost thereof greatly diminish their cost effectiveness.